How, where & why was the E-Mail killed?
I have been testing a bit. Replacing the Google link through a GMX deferrer link results in the same problem. If the attribute value is some link that is not a deferrer, the E-Mail will be sent.
Does the newsletter plugin provide a way of forwarding E-Mails without copy & paste?
Hi, the plugin does not check the content of the email, so it’s probably the provider filtering it. Even wp mail smtp, I believe, ignore the content.
The plugin does not provide a forward functionality, but why you copied an email from Gmail into Newsletter? To create a newsletter? Gmail changes deeply the email content to be correctly (and safely) displayed in a browser, hence the content is not good to create a newsletter.